We are studying the mechanism of oxidation-reduction processes in metalloenzymes, including nitrogenase, nitrate reductase, glutamate synthase, and cytochrome P450 hydroxylases. We are also studying the control of cholesterol metabolism by ACTH in the adrenal cortex, as well as copper metabolism in lymphocytes. We use EPR and other forms of spectroscopy to ascertain the oxidation states and ligands of metal centers in these systems, and we use freeze quench and stopped flow methods to study the time dependence of these processes.